Since the first reports of the production of single-walled carbon nanotubes (hereinafter SWNT) in 1991 by researchers at NEC and IBM, a variety of synthesis routes have been developed to improve both the production rate and the fractional conversion of carbon feedstocks to SWNTs. Among the methods developed for this purpose, all of which are well known and well documented in the art are: Arc Discharge (AD); Pulsed Laser Vaporization (PLV); and Chemical Vapor Deposition (CVD). Much of the work with PLV techniques has been carried out at Rice University as reported by A. Thess et al. in Science 273, 483 (1996). While this work still represents, to the best of our knowledge, the state of the art in the production of high quality SWNTs, it must be noted that the production rates for the processes described by these researchers are only on the order of milligrams per hour. The results of this work and the application of the SWNTs thus produced indicate that there exist many applications for SWNTs, but only if adequately high production rates can be achieved while maintaining the quality of the SWNT, i.e. the integrity of the tube wall.
One such application is as reinforcement for lightweight polymeric structures, especially inflatable structures for use in outer space where in addition to the strength imparting properties of the SWNTs, their electrical conductivity provides a means of reducing static charge buildup on such devices. Other potential applications reside in the areas of hydrogen storage at “low”, i.e. about atmospheric pressure, although debate still rages as to this application and in NEMS or nano electro-mechanical structures useful in, for example, quantum computing devices.
It has been demonstrated that the longer the SWNT the better its properties as a reinforcing agent. Similarly, it is highly desirable that the SWNT “bundles” be small to permit better dispersal in the foregoing reinforcement applications. According to evaluations of SWNTs produced in accordance with the work at Rice University their SWNTs are on the order of 3-5 μm in length and occur in bundles about 10-25 nm in length. Evaluation of SWNTs produced in accordance with the present invention are generally 4-10 μm in length and occur in bundles of from 4-18 nm in length, thus making them more desirable candidates for application in reinforcing applications.
Thus, while there exist numerous areas of potential and actual application for SWNTs, what has been, and is currently lacking, is a method for the production of SWNTs of high quality in sufficient quantities as to provide a reliable and adequate source of desirable raw material for the development and implementation of such applications.
While numerous attempts have been made to improve the production rates of these materials, most such attempts have resulted in the design of carbon nanotube production apparatus and operating procedures that were extremely complex due to operating conditions below atmospheric pressure, required extended heat up and cool down times on the order of hours and/or provided limited flowpaths that could not be readily modified for optimal apparatus operation.
There therefore remains a significant need for an apparatus and operating method that while capable of producing large volumes of carbon nanotubes provide simplified apparatus, greatly reduced heat up and cool down times and flexible flowpaths that can be readily modified for production efficiency optimization.